Molecular Dynamics Simulation for Diffusion of H2/CH4 Mixture in Metal-Organic Framework Zn(tbip)

Abstract

Molecular dynamics simulations were used to study the diffusion of H₂, CH₄ and their equimolarmixtures inmetal-organic framework Zn(tbip) at 298 K. The results were analyzed to obtain the self-diffusivities ( D_s ) and the diffusion selectivities ( S_diff ) of the molecules. In both pure and mixture, the Ds values of H2are in the range of 2.0×10^-8 - 1.0×10^-7 m/s andlarger than that of CH₄, 3.0×10^-9 - 2.0×10^-8 m²/s. In mixtures, the diff S was determined to be different from the Knudsen selectivity ( S_diff,Kn ), giving the values of S_diff / S_diff,Kn in the rage of 1-2.5. This different is attributable to the fact that methaneis more strongly adsorbed than hydrogen at pore walls of Zn(tbip). The S_diff values are in the range of 3-7, indicating that Zn(tbip) can be useful for separating H₂/CH₄ mixtures.